Solvent extraction is used in many industrial processes to recover a desired product that is dissolved in a solvent stream. For example, the mining of copper employs a multi-step solvent extraction process which typically involves the leaching of copper from copper ore using an acidic aqueous solution to form a copper loaded leach liquor. The copper is typically extracted from the leach liquor by an organic solvent mixed with an organic extractant that is specific for copper. The copper loaded organic solvent is then stripped of copper by an acidic aqueous solution to form a copper loaded electrolyte solution. The copper loaded electrolyte solution is then sent to an electrowinning stage, where the copper is electroplated onto a copper cathode.
In order to transfer copper from one solvent to the next as previously described, the two solvents are thoroughly mixed to increase the surface area interface between the two solvent phases. The mixed solvents are then allowed to separate so that the two solvent phases can be transferred to the next stage of the extraction process without cross contamination of downstream solvent streams. In order to achieve phase separation as previously described, the mixed solvent stream is fed into a specially designed settler where the two phases are given enough time to properly separate. The settler is designed to enhance phase separation by providing a solvent flow that is slow in order to reduce turbulence, which has a tendency to remix the two phases. Furthermore, the slow solvent flow allows for an adequate residence time in the settler which assists in phase separation. In addition, the aforementioned settlers attempt to reduce the recirculation of the solvent stream because recirculation can reduce the effective size of the settler.
The aforementioned extraction process can have drawbacks, however. The organic solvent and extractant are relatively expensive, and furthermore, recirculation, which reduces the effective size of the settler, oftentimes results in the use of a larger settler than otherwise would be required. A larger settler has a larger working volume, requiring the use of a larger amount of solvent, which increases costs.
Accordingly, it is desirable to provide a method and apparatus for separation that produces little recirculation while providing a decelerated, unidirectional flow. It is further desirable to provide a cost efficient settler apparatus having an effective operational volume.